Cumulative flying time and risk of venous thromboembolism

A Comprehensive Review of Risk Factors for Venous Thromboembolism: From Epidemiology to Pathophysiology

Venous thromboembolism (VTE) is the third most common cause of death worldwide. The incidence of VTE varies according to different countries, ranging from 1-2 per 1000 person-years in Western Countries, while it is lower in Eastern Countries (<1 per 1000 person-years). Many risk factors have been identified in patients developing VTE, but the relative contribution of each risk factor to thrombotic risk, as well as pathogenetic mechanisms, have not been fully described. Herewith, we provide a comprehensive review of the most common risk factors for VTE, including male sex, diabetes, obesity, smoking, Factor V Leiden, Prothrombin G20210A Gene Mutation, Plasminogen Activator Inhibitor-1, oral contraceptives and hormonal replacement, long-haul flight, residual venous thrombosis, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, trauma and fractures, pregnancy, immobilization, antiphospholipid syndrome, surgery and cancer. Regarding the latter, the incidence of VTE seems highest in pancreatic, liver and non-small cells lung cancer (>70 per 1000 person-years) and lowest in breast, melanoma and prostate cancer (<20 per 1000 person-years). In this comprehensive review, we summarized the prevalence of different risk factors for VTE and the potential molecular mechanisms/pathogenetic mediators leading to VTE.

Travel-Associated Venous Thromboembolism

INTRODUCTION

Long-distance travel is assumed to be a risk factor for venous thromboembolism (VTE). However, the available data have not clearly demonstrated the strength of this relationship, nor have they shown evidence for the role of thromboprophylaxis.

METHODS

We performed a systematic review of the literature. We also summarized available guidelines from 5 groups.

RESULTS

We found 18 studies that addressed this question. Based on the data presented in the review, we conclude that there is an association between VTE and length of travel, but this association is mild to moderate in effect size with odds ratios between 1.1 and 4. A dose-response relationship between VTE and travel time was identified, with a 26% higher risk for every 2 h of air travel (P=0.005) starting after 4 h. The quality of evidence for both travel length and thromboprophylaxis was low. However, low-risk prophylactic measures such as graduated compression stockings were shown to be effective in VTE prevention. There is heterogeneity among the different practice guidelines. The guidelines generally concur that no prophylaxis is necessary in travelers without known thrombosis risk factors and advocate for conservative treatment such as compression stockings over pharmacologic prophylaxis.

CONCLUSIONS

We conclude air travel is a risk factor for VTE and that there is a dose relationship starting at 4 h. For patients with risk factors, graduated compression stockings are effective prophylaxis.

The secret enemy during a flight: Economy class syndrome

Deep venous thrombosis (DVT) and pulmonary thromboembolism (PTE) are the major causes of morbidity and mortality in immobile patients. There is observational evidence that intercontinental air travel is associated with a high incidence of DVT and PTE during or within 48 hours of long-distance flights. This situation is known as the economy class syndrome and can affect both the cabin crew and passengers. The term "economy class syndrome" refers to the occurrence of thrombotic events that mainly occur in passengers in the economy class of the aircraft during long-haul flights. This syndrome results from several factors related to the aircraft cabin and the passenger, acting together to predispose to excessive blood coagulation, which can result in venous thromboembolism. In this review, we have shared the relationship between air travel and the formation of DVT and PTE.

Medical Events on Board Aircraft: Reducing Confusion and Misinterpretation in the Scientific Literature

INTRODUCTION: A topic in aviation medicine that attracts much attention from the scientific community as well as from the media concerns medical incidents on board commercial airline flights. It was noticed that many papers on the subject were written by authors whose specialization was outside that of aviation medicine and that they sometimes made basic errors concerning the application of scientific principles of the subject. A review was undertaken to determine if there were any patterns to the observed errors and, if so, to consider whether recommendations might be provided that could reduce their frequency.METHOD: A literature search was undertaken of MEDLINE using PubMed for English-only articles published between January 1, 1974, and February 1, 2019, employing the following search terms: air emergency, air emergencies, air passenger, air travel, aircraft, airline, aviation, commercial air, flight, and fitness to fly. In addition, other relevant papers held in the personal collection of the authors were reviewed.RESULTS: Many cases of misinterpretation or misunderstanding of aviation medicine were found, which could be classified into eight main categories: references; cabin altitude; pressure/volume relationship; other technical aspects of aircraft operations; regulations; medical events; in-flight deaths; and automated external defibrillator.CONCLUSION: Papers were identified as having questionable statements of fact or of emphasis. Such instances often appeared to result from authors being unfamiliar with the subject of aviation medicine and/or the commercial aviation environment. Simple steps could be taken by authors to reduce the future rate of such instances and recommendations are provided.Thibeault C, Evans AD. Medical events on board aircraft: reducing confusion and misinterpretation in the scientific literature. Aerosp Med Hum Perform. 2021; 92(4):265273.

Economy class syndrome: what is it and who are the individuals at risk?

The term ‘economy class syndrome’ refers to the occurrence of thrombotic events during long-haul flights that mainly occur in passengers in the economy class of the aircraft. This syndrome results from several factors related to the aircraft cabin (immobilization, hypobaric hypoxia and low humidity) and the passenger (body mass index, thrombophilia, oral contraceptives or hormone replacement therapy, cancer), acting together to predispose to excessive blood coagulation, which can result in venous thromboembolism. Several risk factors, both genetic and acquired, are associated with venous thromboembolism. The most important genetic risk factors are natural anticoagulant deficiencies (antithrombin, protein C and protein S), factor V Leiden, prothrombin and fibrinogen gene mutations and non-O blood group individuals. Acquired risk factors include age, pregnancy, surgery, obesity, cancer, hormonal contraceptives and hormone replacement therapy, antiphospholipid syndrome, infections, immobilization and smoking. People who have these risk factors are predisposed to hypercoagulability and are more susceptible to suffer venous thromboembolism during air travel. For these individuals, a suitable outfit for the trip, frequent walks, calf muscle exercises, elastic compression stockings and hydration are important preventive measures. Hence, it is essential to inform about economic class syndrome in an attempt to encourage Brazilian health and transport authorities to adopt measures, in partnership with the pharmaceutical industry, to prevent venous thromboembolism.

Characteristics of provoked deep venous thrombosis in a tertiary care center

OBJECTIVE

Provoked deep venous thrombosis (DVT) is precipitated by a specific event. This paper compares the characteristics of provoked DVT in patients with transient risk (TR) factors and patients with continuous risk (CR) factors.

METHODS

A retrospective review of records of all consecutive patients diagnosed with DVT between January 2013 and August 2014 was performed. Patients with provoked DVT were included in the TR group if the provoking event resolved in 2 weeks and they did not have ongoing risk of thrombosis. Patients in the CR group had a provoked DVT with ongoing risk of thrombosis due to individual factors deemed to be ongoing risks of thrombosis, such as cancer, hypercoagulable disorder, and prolonged immobilization. Demographics, risk factors, association with pulmonary embolism (PE) and its severity, risk of recurrent venous thromboembolism (VTE), and mortality were compared between the two groups.

RESULTS

A total of 838 patients were diagnosed with DVT, and 50.7% (425) were provoked. There were 127 (29.9%) patients with TR and 298 (70.1%) with CR. TR patients were younger (60.4 ± 16.3 vs 65.9 ± 16.0; P = .001). TR was more likely to be provoked by surgery (70.9% vs 55.4%; P = .003), whereas CR was more likely to be provoked by immobilization (21.5% vs 12.6%; P = .032). CR patients were affected by cancer (48.7%) and hypercoagulable disorders (4.4%). TR patients were more likely to have calf DVTs (36.2% vs 26.2%; P = .047). There was a trend toward lower association with PE on presentation in TR (17.3% vs 21.1%; P = .072), but that did not reach statistical significance. However, TR factors were more likely to be associated with low-risk PE compared with CR factors (30.2% vs 54.6%; P = .040). After mean follow-up of 7.2 months, CR had higher risk of recurrent VTE (14.0% vs 6.8%; P = .045) and mortality (23.5% vs 7.1%; P < .0001).

CONCLUSIONS

Provoked DVT with CR factors affects older patients and is associated with high recurrence of VTE and mortality compared with provoked DVT with TR factors.

Fitness to fly in patients with lung disease

Patients with chronic lung disease may have mild hypoxemia at sea level. Some of these cases may go unrecognized, and even among those who are known to be hypoxemic, some do not use supplemental oxygen. During air travel in a hypobaric hypoxic environment, compensatory pulmonary mechanisms may be inadequate in patients with lung disease despite normal sea-level oxygen requirements. In addition, compensatory cardiovascular mechanisms may be less effective in some patients who are unable to increase cardiac output. Air travel also presents an increased risk of venous thromboembolism. Patients with cystic lung disease may also be at increased risk of pneumothorax. Although overall this risk appears to be relatively low, should a pneumothorax occur, it could present a significant challenge to the patient with chronic lung disease, particularly if hypoxemia is already present. As such, a thorough assessment of patients with chronic lung disease and cardiac disease who are contemplating air travel should be performed. The duration of the planned flight, the anticipated levels of activity, comorbid illnesses, and the presence of risk factors for venous thromboembolism are important considerations. Hypobaric hypoxic challenge testing reproduces an environment most similar to that encountered during actual air travel; however, it is not widely available. Assessment for hypoxia is otherwise best performed using a normobaric hypoxic challenge test. Patients in need of supplemental oxygen need to contact the airline and request this accommodation during flight. They should also be advised on arranging portable oxygen concentrators before air travel, and a discussion of the potential risks of travel should take place.